// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_MAYBE_HANDLES_H_
#define V8_MAYBE_HANDLES_H_

#include <type_traits>

#include "src/handles.h"

namespace v8 {
namespace internal {

    // ----------------------------------------------------------------------------
    // A Handle can be converted into a MaybeHandle. Converting a MaybeHandle
    // into a Handle requires checking that it does not point to nullptr.  This
    // ensures nullptr checks before use.
    //
    // Also note that Handles do not provide default equality comparison or hashing
    // operators on purpose. Such operators would be misleading, because intended
    // semantics is ambiguous between Handle location and object identity.
    template <typename T>
    class MaybeHandle final {
    public:
        V8_INLINE MaybeHandle() = default;

        // Constructor for handling automatic up casting from Handle.
        // Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected.
        template <typename S, typename = typename std::enable_if<std::is_convertible<S*, T*>::value>::type>
        V8_INLINE MaybeHandle(Handle<S> handle)
            : location_(handle.location_)
        {
        }

        // Constructor for handling automatic up casting.
        // Ex. MaybeHandle<JSArray> can be passed when Handle<Object> is expected.
        template <typename S, typename = typename std::enable_if<std::is_convertible<S*, T*>::value>::type>
        V8_INLINE MaybeHandle(MaybeHandle<S> maybe_handle)
            : location_(maybe_handle.location_)
        {
        }

        V8_INLINE MaybeHandle(T object, Isolate* isolate);

        V8_INLINE void Assert() const { DCHECK_NOT_NULL(location_); }
        V8_INLINE void Check() const { CHECK_NOT_NULL(location_); }

        V8_INLINE Handle<T> ToHandleChecked() const
        {
            Check();
            return Handle<T>(location_);
        }

        // Convert to a Handle with a type that can be upcasted to.
        template <typename S>
        V8_INLINE bool ToHandle(Handle<S>* out) const
        {
            if (location_ == nullptr) {
                *out = Handle<T>::null();
                return false;
            } else {
                *out = Handle<T>(location_);
                return true;
            }
        }

        // Returns the raw address where this handle is stored. This should only be
        // used for hashing handles; do not ever try to dereference it.
        V8_INLINE Address address() const
        {
            return reinterpret_cast<Address>(location_);
        }

        bool is_null() const { return location_ == nullptr; }

    protected:
        Address* location_ = nullptr;

        // MaybeHandles of different classes are allowed to access each
        // other's location_.
        template <typename>
        friend class MaybeHandle;
    };

    // A handle which contains a potentially weak pointer. Keeps it alive (strongly)
    // while the MaybeObjectHandle is alive.
    class MaybeObjectHandle {
    public:
        inline MaybeObjectHandle();
        inline MaybeObjectHandle(MaybeObject object, Isolate* isolate);
        inline MaybeObjectHandle(Object object, Isolate* isolate);
        inline explicit MaybeObjectHandle(Handle<Object> object);

        static inline MaybeObjectHandle Weak(Object object, Isolate* isolate);
        static inline MaybeObjectHandle Weak(Handle<Object> object);

        inline MaybeObject operator*() const;
        inline MaybeObject operator->() const;
        inline Handle<Object> object() const;

        bool is_identical_to(const MaybeObjectHandle& other) const
        {
            Handle<Object> this_handle;
            Handle<Object> other_handle;
            return reference_type_ == other.reference_type_ && handle_.ToHandle(&this_handle) == other.handle_.ToHandle(&other_handle) && this_handle.is_identical_to(other_handle);
        }

        bool is_null() const { return handle_.is_null(); }

    private:
        inline MaybeObjectHandle(Object object,
            HeapObjectReferenceType reference_type,
            Isolate* isolate);
        inline MaybeObjectHandle(Handle<Object> object,
            HeapObjectReferenceType reference_type);

        HeapObjectReferenceType reference_type_;
        MaybeHandle<Object> handle_;
    };

} // namespace internal
} // namespace v8

#endif // V8_MAYBE_HANDLES_H_
